Semiconducter device with filler to suppress generation of air bubbles and electric power converter

ABSTRACT

A semiconductor device including: an insulating substrate having a conductor layer on the upper face and the lower face and a semiconductor element mounted on the upper conductor layer; a base plate bonded to the lower conductor layer; a case member surrounding the insulating substrate and bonded to the surface of the base plate to which the conductor layer bonded to the lower face; a first filler being a silicone composition filled in a region surrounded by the base plate and the case member; and a second filler being injected into a region below the first filler and surrounding a peripheral edge portion of the insulating substrate, whose height from the base plate is higher than the upper face and is lower than a bonding face between the semiconductor element and the upper conductor layer.

TECHNICAL FIELD

The present invention relates to a filling structure of a semiconductordevice in which a power semiconductor element is sealed with a filler,and to an electric power converter using the semiconductor device.

BACKGROUND ART

A semiconductor element of a type in which an energization path isformed in a vertical direction of the element for the purpose of copingwith a high voltage and a large current is generally called a powersemiconductor element (for example, an insulated gate bipolar transistor(IGBT), a metal oxide semiconductor field effect transistor (MOSFET), abipolar transistor, or a diode). A semiconductor device in which thepower semiconductor element is mounted on a circuit board and packagedwith a filler is used in various fields, such as industrial equipment,vehicles, and railways. In recent years, along with increase inperformance of equipment having the semiconductor device mountedthereon, there is more demand for increase in performance of thesemiconductor device, such as increase in rated voltage and ratedcurrent or enlargement of a usage temperature range (to highertemperature or lower temperature).

A mainstream packaging structure of the semiconductor device is called acase-type packaging structure. The semiconductor device using thecase-type packaging structure has the following structure. The powersemiconductor element is mounted on a heat-radiating base plate throughthe intermediation of an insulating circuit board. The insulatingcircuit board includes a front-face electrode pattern on one face of aninsulating substrate, and a back-face electrode pattern on another faceof the insulating substrate. A case is caused to adhere to the baseplate. Further, the semiconductor element mounted in the semiconductordevice is connected to main electrodes. Bonding wires are used for theconnection between the semiconductor element and the main electrodes.For the purpose of preventing insulation failure that occurs when a highvoltage is applied, in general, an insulating gel-like filler astypified by a silicone gel is used as the filler of the semiconductordevice.

In general, the amount of gas that can be dissolved in the silicone gelis decreased as the temperature is increased. Therefore, when the usagetemperature range of the semiconductor device is enlarged and thesilicone gel is used at higher temperature, the gas that has becomeinsoluble in the silicone gel forms air bubbles. In a portion in whichsuch air bubbles are generated, the insulation filling effect by thesilicone gel cannot be obtained, and hence the insulation performance ofthe semiconductor device is degraded.

Further, the semiconductor device incorporates many members such as asemiconductor element, a bonding material, and a wire. Even whendegassing processing is performed when the silicone gel is injected,there is a risk that air bubbles may be generated in the semiconductordevice.

Further, those air bubbles in the silicone gel are assumed to beincreased in size due to influences of external environments such asmoisture absorption and heating.

As a countermeasure fora case in which air bubbles are generated in thesilicone gel as described above or a case in which the silicone gel isseparated from various members, it is conceivable to inject a rubbermaterial in which air bubbles cannot be generated or grown into thematerial when the semiconductor device is used. The rubber material isinjected into a narrow gap space between a surface portion at which aceramic substrate of the insulating circuit board, for which aninsulation property is required to be secured, is exposed and the baseplate to which the insulating circuit board is bonded.

As a related-art semiconductor device, there is disclosed asemiconductor device having a structure in which a peripheral edgeportion of the insulating circuit board is covered with a siliconerubber adhesive, which has a strong adhesive property with respect tothe insulating substrate and a container bottom face, and then a filleris injected (for example, Patent Literature 1).

CITATION LIST Patent Literature

[PTL 1] JP 8-125071 A (page 4, FIG. 1)

SUMMARY OF INVENTION Technical Problem

However, in the semiconductor device described in Patent Literature 1,the peripheral edge portion of the insulating circuit board is coveredwith an adhesive material, and hence, when the exposed part of theceramic substrate of the insulating circuit board, that is, a creepagedistance is large, a narrow gap is formed between the base plate and asurface portion on the back face side of the exposed part of the ceramicsubstrate. It is difficult to inject an adhesive having high viscosityinto this narrow gap region. Air bubbles may be generated when anadhesive having high viscosity is injected, and thus insulationreliability is degraded in some cases.

The present invention has been made to solve the above-mentionedproblems.

Solution to Problem

According to one embodiment of the present invention, there is provideda semiconductor device including: an insulating substrate having aconductor layer formed on each of an upper face and a lower face of theinsulating substrate, the conductor layer on the upper face having asemiconductor element mounted thereon; a base plate bonded to theconductor layer on the lower face; a case member surrounding theinsulating substrate and adhering to a face of the base plate to whichthe conductor layer on the lower face is bonded; a first filler being asilicone composition injected into a region surrounded by the base plateand the case member; and a second filler being a silicone compositionthat is harder than the first filler, the second filler surrounding aperipheral edge portion of the insulating substrate below the firstfiller in the region, the second filler being injected into a region inwhich a height from the base plate is higher than the upper face and islower than a bonding face between the semiconductor element and theconductor layer on the upper face.

Advantageous Effects of Invention

According to one embodiment of the present invention, in thesemiconductor device having a narrow gap, generation of air bubbles canbe suppressed, and thus insulation reliability can be improved.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic top structure view for illustrating asemiconductor device according to a first embodiment of the presentinvention.

FIG. 2 is a schematic sectional structure view for illustrating thesemiconductor device according to the first embodiment of the presentinvention.

FIG. 3 is a schematic sectional structure view for illustrating an endportion of an insulating circuit board excluding a filler in thesemiconductor device according to the first embodiment of the presentinvention.

FIG. 4 is a schematic sectional structure view for illustrating afilling state at the end portion of the insulating circuit board in thesemiconductor device according to the first embodiment of the presentinvention.

FIG. 5 is a schematic top structure view for illustrating asemiconductor device according to a second embodiment of the presentinvention.

FIG. 6 is a schematic sectional structure view for illustrating thesemiconductor device according to the second embodiment of the presentinvention.

FIG. 7 is a schematic sectional structure view for illustrating a spacebetween two insulating circuit boards in the semiconductor deviceaccording to the second embodiment of the present invention.

FIG. 8 is a schematic top structure view for illustrating asemiconductor device according to a third embodiment of the presentinvention.

FIG. 9 is a schematic sectional structure view for illustrating thesemiconductor device according to the third embodiment of the presentinvention.

FIG. 10 is a schematic top structure view for illustrating anothersemiconductor device according to the third embodiment of the presentinvention.

FIG. 11 is a schematic sectional structure view for illustrating theanother semiconductor device according to the third embodiment of thepresent invention.

FIG. 12 is a schematic top structure view for illustrating a partitionwall of the semiconductor device according to the third embodiment ofthe present invention.

FIG. 13 is a block diagram for illustrating a configuration of a powerconversion system to which an electric power converter according to afourth embodiment of the present invention is applied.

FIG. 14 is a schematic sectional structure view for illustrating afilling height of silicone rubber at a peripheral edge portion of aninsulating circuit board in embodiments of the present invention.

DESCRIPTION OF EMBODIMENTS First Embodiment

FIG. 1 is a schematic top structure view for illustrating asemiconductor device according to a first embodiment of the presentinvention. FIG. 2 is a schematic sectional structure view forillustrating the semiconductor device according to the first embodimentof the present invention. FIG. 1 is a view for illustrating asemiconductor device 100 as viewed from the top through a first filler 9being a silicone composition. A peripheral edge portion (outerperipheral portion) of an insulating substrate 52, which is covered witha second filler 10, is indicated by the dotted line.

FIG. 2 is a schematic sectional structure view taken along thedash-dotted line A-A of FIG. 1. In FIG. 2, the semiconductor device 100includes a base plate 1, a case member 2, solder 3 serving as a bondingmaterial, semiconductor elements 4, an insulating circuit board 5,bonding wires 6 serving as wiring members, electrode terminals 7, a lidmember 8, the first filler 9 being a silicone composition, the secondfiller 10 being a silicone composition, electrode patterns 51 and 53serving as conductor layers, and the insulating substrate 52.

The insulating circuit board 5 includes the insulating substrate 52, theelectrode pattern 51 formed on an upper face (front face) side of theinsulating substrate 52, and the electrode pattern 53 formed on a lowerface (back face) side of the insulating substrate 52. On the electrodepattern 51 formed on the upper face side of the insulating substrate 52,the semiconductor elements 4 are electrically bonded via the solder orother bonding materials 3. In this case, for example, as thesemiconductor element 4, a power control semiconductor element(switching element) such as a MOSFET, which is configured to control alarge current, or a diode for free-wheeling (free-wheeling diode) isused.

Further, in the insulating circuit board 5, the electrode pattern 53formed on the lower face side of the insulating substrate 52 is fixed tothe base plate 1 via the solder or other bonding materials 3. Further,the base plate 1 serves as a bottom plate of the semiconductor device100 so as to form a region (hereinafter referred to as “case”)surrounded by the base plate 1 and the case member 2 arranged at theperiphery of the base plate 1.

For the purpose of securing an insulation property inside the regionsurrounded by the case member 2 of the semiconductor device 100, thefirst filler 9 being a silicone composition and the second filler 10being a silicone composition are injected into the case. The firstfiller 9 being a silicone composition is, for example, a silicone gel,and is injected up to a height that allows the semiconductor elements 4and the bonding wires 6 to be sealed with the silicone gel.

Further, the second filler 10 being a silicone composition injectedbelow the silicone gel 9 in the case is, for example, silicone rubber,and is injected so as to surround a peripheral edge portion of theinsulating substrate 52. The silicone rubber 10 is injected up to afilling height position that is higher than an upper face of theinsulating substrate 52 from a front face of the base plate 1, and islower than a bonding face between the semiconductor element 4 and thesolder 3, that is, a mounting face (mounting portion) of thesemiconductor element 4, which is an upper face of the electrode pattern51 formed on the upper face side of the insulating substrate 52.

At this time, the silicone rubber 10 surrounds the peripheral edgeportion of the insulating substrate 52, and fills (encapsulates) anexposed part of the insulating substrate 52. The silicone rubber 10 isinjected up to the same height in a space between the plurality ofelectrode patterns 51 formed on the upper face of the insulatingsubstrate 52.

Further, the silicone gel 9 is injected onto the silicone rubber 10 sothat the case is filled with the filler.

To the semiconductor element 4, the bonding wire 6 or other wiring forelectrically connecting an electrode of the semiconductor element 4 tothe outside is connected. Further, the bonding wire 6 is connected tothe electrode terminal 7 so as to be electrically connected to theoutside of the case. The electrode terminal 7 is insert-molded oroutsert-molded to the case member 2.

The lid member 8 is arranged on an upper portion side of the case member2 (opposite side of a side in contact with the base plate 1). With thelid member 8, the inside and the outside of the semiconductor device 100are separated from each other so that powder dust or the like isprevented from entering the inside of the semiconductor device 100. Thelid member 8 is fixed to the case member 2 with an adhesive (not shown)or screws (not shown).

Details of the components are described below.

As the semiconductor element 4, when a semiconductor element using asemiconductor material that operates at 150° C. or more is employed, aneffect of suppressing generation of air bubbles is large. In particular,a large effect can be obtained when there is employed a so-called widebandgap semiconductor, which is formed of a material such as siliconcarbide (SiC), a gallium nitride (GaN) based material, or diamond (C) tohave a wider bandgap than that of silicon (Si).

Further, in FIG. 2, as an example, only two semiconductor elements 4 aremounted in one filled semiconductor device 100, but the number ofsemiconductor elements 4 is not limited thereto. A required number ofsemiconductor elements 4 can be mounted depending on the application tobe used.

The solder 3 is used as the bonding material, but the bonding materialis not limited thereto. The semiconductor element 4 and the electrodepattern 51, or the electrode pattern 53 and the base plate 1 may bebonded to each other with use of silver or a silver alloy.

In general, copper is used for the electrode pattern 51 (front face),the electrode pattern 53 (back face), the base plate 1, and theelectrode terminals 7, but the material for those components is notlimited thereto. It is only required that the material have requiredheat radiation characteristics. For example, aluminum, iron, or acomposite material of those materials may be used. Further,copper/invar/copper or other composite materials may be used, or AlSiC,CuMo, or other alloys may be used.

Further, in general, nickel plating is performed on the faces of theelectrode pattern 51 (front face), the electrode pattern 53 (back face),the base plate 1, and the electrode terminal 7, but the presentinvention is not limited thereto. Gold or tin plating may be performed.It is only required to obtain a structure capable of supplying requiredcurrent and voltage to the semiconductor element 4.

Further, at least parts of the electrode terminal 7 and the electrodepattern 51 are embedded in the silicone gel 9, and hence fine unevennessmay be formed on the faces of the electrode terminal 7 and the electrodepattern 51 in order to improve the adhesiveness between the silicone gel9 and the electrode terminal 7 and between the silicone gel 9 and theelectrode pattern 51. With this unevenness, the adhesiveness between thesilicone gel 9 and the electrode terminal 7 and between the silicone gel9 and the electrode pattern 51 can be improved.

The insulating circuit board 5 is obtained by forming the electrodepatterns 51 and 53 made of copper or aluminum on both faces of theinsulating substrate 52 made of ceramics such as Al₂O₃, SiO₂, AlN, BN,and Si₃N₄. The insulating circuit board 5 is required to have a heatradiation property and an insulation property, and may be made ofmaterials other than the above-mentioned materials. The electrodepatterns 51 and 53 may be formed on the insulating substrate 52 being,for example, a resin cured product in which ceramic powder is dispersedor a resin cured product in which a ceramic plate is embedded.

Further, when the insulating substrate 52 is a resin cured product inwhich ceramic powder is dispersed, the ceramic powder used for theinsulating substrate 52 is Al₂O₃, SiO₂, AlN, BN, Si₃N₄, or the like, butthe powder is not limited thereto. Diamond, SiC, B₂O₃, or the like maybe used. Further, powder made of a silicone resin, an acrylic resin, orother resins may be used.

The powder to be used often has a sphere shape, but the shape is notlimited thereto. Powder having a milled shape, a granular shape, or aflake shape, or powder being an aggregate may be used. As a powderadding amount, an amount of powder with which a required heat radiationproperty and a required insulation property can be obtained may beadded. As the resin to be used for the insulating substrate 52, ingeneral, an epoxy resin is used, but the resin is not limited thereto. Apolyimide resin, a silicone resin, an acrylic resin, or other resins maybe used. Any material can be used as long as the material has both of aninsulation property and an adhesive property.

As the bonding wire 6, a wire member having a circular cross section andbeing made of aluminum or gold is used, but the bonding wire 6 is notlimited thereto. For example, a member obtained by forming a copperplate having a square cross section into a band shape (ribbon) may beused. The material of the bonding wire 6 may be an aluminum alloy.

As illustrated in FIG. 2, in the first embodiment, four bonding wires 6are used to establish connections between the semiconductor elements 4,between the semiconductor element 4 and the electrode terminal 7,between the semiconductor element 4 and the electrode pattern 51, andbetween the electrode pattern 51 and the electrode terminal 7, but thepresent invention is not limited thereto. A required number of bondingwires 6 having required thicknesses (sizes) may be provided dependingon, for example, a current density of the semiconductor element 4.

Further, as a method and structure for bonding the bonding wire 6 and abonded portion, melted metal bonding in which a metal piece of copper,tin, or the like is melted, ultrasonic bonding, or other methods can beused. However, the method and the structure are not particularly limitedas long as required current and voltage can be supplied to thesemiconductor element 4.

The case member 2 is preferred to be made of a resin material having ahigh thermal softening point, and is made of, for example, apolyphenylene sulfide (PPS) resin. However, the material is notparticularly limited as long as the material has an insulation propertyand does not thermally deform within a usage temperature range of thesemiconductor device 100.

As the first filler, for example, the silicone gel 9 is used, but thefirst filler is not limited thereto. Any material can be used as long asthe material has a desired elastic modulus and a desired heatresistance. For example, a urethane resin having both of an insulationproperty and an adhesive property may be used.

As the hardness of the silicone gel 9 being the first filler, when ahard silicone gel 9 having a penetration of 20 or less is used, thebonding wire 6 may be damaged due to expansion and contraction of thesilicone gel 9 at the time of a heat cycle test of the semiconductordevice 100. Therefore, the hardness is desired to be 20 or more inpenetration. In contrast, when a soft silicone gel 9 having apenetration of 100 or more is used, the silicone gel 9 itself is damageddue to expansion and contraction of the silicone gel 9 at the time ofthe heat cycle test of the semiconductor device 100. Therefore, thehardness is desired to be 100 or less in penetration. As a result, inorder to secure reliability of the semiconductor device 100, thesilicone gel 9 is desired to have hardness in a range of 20 or more and100 or less in penetration.

FIG. 3 is a schematic sectional structure view for illustrating an endportion of the insulating circuit board of the semiconductor deviceexcluding the filler in the first embodiment of the present invention.In FIG. 3, the insulating circuit board 5 includes the insulatingsubstrate 52, the electrode pattern 51 formed on the upper face side ofthe insulating substrate 52, and the electrode pattern 53 formed on thelower face side of the insulating substrate 52. To the upper face of theelectrode pattern 51, the semiconductor element 4 is bonded via thesolder 3 or other bonding materials (not shown, see FIG. 1 and FIG. 2).The lower face of the electrode pattern 53 is bonded to the base plate 1with the solder 3 or other bonding materials.

In order for the semiconductor device 100 to maintain (secure) arequired dielectric breakdown voltage, on the upper face side of theinsulating substrate 52, the electrode pattern 51 is formed with amargin portion (surface portion) being left at the outer periphery ofthe insulating substrate 52. Further, on the lower face side of theinsulating substrate 52, the electrode pattern 53 is formed with amargin portion (surface portion) being left at the outer periphery ofthe insulating substrate 52.

The surface portions on the upper face side and the lower face side ofthe insulating substrate 52 are formed so as to secure the insulationproperty between the electrode pattern 51 and the electrode pattern 53of the insulating circuit board 5. Along with increase in breakdownvoltage of the semiconductor device 100, the creepage distance and thethickness of the insulating substrate 52 are required to be increased.The surface portion herein refers to an outer peripheral portion regionof the insulating substrate 52 in which the electrode patterns 51 and 53are not formed.

A length of the surface portion on the upper face side of the insulatingsubstrate 52 is represented by L1, a length of the surface portion onthe lower face side of the insulating substrate 52 is represented by L2,a length of a side surface of the insulating substrate 52, that is, athickness of the insulating substrate 52 is represented by L3, athickness of the electrode pattern 53 is represented by L4, a thicknessof the solder 3 is represented by L5, and a length from the end portionof the insulating substrate 52 to the case member 2 is represented byL6. In this case, as a path in which dielectric breakdown occurs in thesemiconductor device 100, an insulation distance of L1+L3+L4+L5 or aninsulation distance of L1+L3+L2 is conceivable.

The dielectric breakdown occurs in a dominant manner in any path havinga shorter distance. Therefore, the lengths of L1, L2, L3, L4, and L5 areonly required to be set so that the semiconductor device 100 can securean insulation distance satisfying the dielectric breakdown voltage.Further, L6 is generally a distance of 2 mm or more in consideration ofmisalignment at the time of bonding between the insulating circuit board5 and the base plate 1. In a case where L6 is 2 mm or less, when theinsulating circuit board 5 is arranged on the base plate 1, theinsulating circuit board 5 cannot be arranged at a predeterminedposition due to a shift during alignment. When L6 is 10 mm or more, aratio of the silicone rubber 10 occupied in the case is increased, whichcauses occurrence of stress. Thus, the silicone rubber 10 may beseparated from the base plate 1. For those reasons, the dimension of L6is set in a range of 2 mm or more and 10 mm or less so that asemiconductor device having secured insulation reliability can beconfigured.

In a general semiconductor device, in general, a space S1 between thesurface portion on the lower face side of the insulating substrate 52and a surface on the upper side of the base plate 1 on which theinsulating circuit board 5 is mounted is filled with the silicone gel 9.The electrode patterns 51 and 53 are generally bonded to the insulatingsubstrate 52 with a brazing filler metal. At a brazing filler metalportion at an interface between the electrode pattern 51 or 53 and theinsulating substrate 52 or at a bonding material interface at which theelectrode pattern 53 and the base plate 1 are bonded with the bondingmaterial 3, an unfilled part in which the silicone gel 9 is not fullyinjected is liable to occur.

Further, even when degassing processing is performed at the time whenthe silicone gel 9 is injected, at the surface portion on the lower faceside of the insulating circuit board 5, air bubbles formed in the spaceS1 may not be fully removed from the inside of the space S1 to theoutside of the space 51 because the surface portion of the insulatingsubstrate 52 serves as an eave. Thus, the air bubbles are liable toremain as voids when the silicone gel 9 is cured. The voids remaining inthe silicone gel 9 are expanded and contracted along with the heat cycleof the silicone gel 9. Further, when the voids adsorb water and then areheated at high temperature due to a high-temperature operation of thesemiconductor device, the adsorbed water is vaporized, and henceenlargement of the air bubbles is promoted in the silicone gel 9.

A diameter of the enlarged air bubble in the silicone gel 9 isrepresented by R1. In this case, the air bubble reduces the insulationdistance, and hence, when an air bubble is generated in the silicone gel9 present in the space S1, each of the insulation distance L1+L3+L4+L5and the insulation distance L1+L3+L2, which has originally beenresponsible for the insulation property, is decreased by the amount ofthe air-bubble size R1. Thus, the effective insulation distance becomesthe insulation distance L1+L3+L4+L5−R1 and the insulation distanceL1+L3+L2−R1. The insulation distance is reduced by the amount of thediameter of the air bubble, and thus the insulation performance of thesemiconductor device is degraded.

The degradation of the insulation performance of the semiconductordevice is caused not only by the air bubbles generated only in the spaceS1 on the lower face side of the insulating substrate 52. Thedegradation of the insulation performance is similarly caused by airbubbles initially generated on the upper face side of the insulatingsubstrate 52, in the vicinity of the case member 2, and in the vicinityof the semiconductor element 4 when the air bubbles reach the surfaceportion of the insulating circuit board 5.

FIG. 4 is a schematic sectional structure view for illustrating afilling state at the end portion of the insulating circuit board in thesemiconductor device according to the first embodiment of the presentinvention. The space S1 below the insulating substrate 52 is filled notwith the silicone gel 9 but with the silicone rubber 10 so thatgeneration of air bubbles, which have been generated in the silicone gel9, can be suppressed. When only the silicone gel 9 is used, the hardnessas the filler is low, and hence the air bubbles are enlarged with highpossibility due to, for example, increase in internal pressure of theair bubbles in the filler material. In contrast, when the siliconerubber 10 is used, the hardness as the filler is high, and hencegeneration of the air bubbles can be suppressed.

Further, the silicone rubber 10 has, as compared to the silicone gel 9,a higher adhesive property with respect to various members such as theinsulating substrate 52 and the base plate 1 and lower transmittance ofgas and moisture. Therefore, the insulation reliability can be enhancedin the space 51, for which the insulation property is required.

Further, even when air bubbles are generated and enlarged in thesilicone gel 9 arranged above the silicone rubber 10, entrance of theair bubbles into the region of the space S1 filled with the siliconerubber 10 can be suppressed. In this manner, degradation of theinsulation reliability due to generation of air bubbles in the siliconegel 9 can be suppressed.

Regarding the filling amount of the silicone rubber 10, the bonding wire6 is bonded on the electrode pattern 51 formed on the upper face side ofthe insulating substrate 52, and hence, when the bonding wire 6 iscovered with a filler material having high hardness, there is a risk ofdamaging of the bonding wire 6 along with the heat cycle test of thesemiconductor device 100. Therefore, the filling height from the baseplate 1 of the silicone rubber 10 is desired to be lower than the frontface being the mounting face of the electrode pattern 51, on which thesemiconductor element 4 is mounted, and at least the space S1 requiringthe dielectric breakdown voltage is required to be entirely filled withthe silicone rubber 10. It is desired to cover a region represented bythe dimensions L1, L2, and L3, which corresponds to a surface portion ofthe insulating substrate 52 that may be a starting point of generationof air bubbles and is present at a bonding interface between theinsulating substrate 52 and the electrode patterns 51 and 53.

Along with the enlargement of the usage temperature range of thesemiconductor device 100 (to higher temperature or lower temperature),the silicone rubber 10 is more expanded or contracted as compared to therelated art by the heat cycle. When the area of the silicone rubber 10covering the base plate 1 is large, with the high stress generated dueto expansion or contraction of the silicone rubber 10, there is a riskthat the silicone rubber 10 may be separated from various members due toa difference in linear expansion coefficient between the silicone rubber10 and various members such as the base plate 1 and the solder 3 orother bonding materials.

For example, the linear expansion coefficient of the silicone rubber 10is generally from 300 ppm/K to 400 ppm/K. When the hardness of thesilicone rubber 10 is higher than 70 in Shore A hardness, separationbetween the silicone rubber 10 and various members is liable to occur.

Further, even when separation between the silicone rubber 10 and thevarious members does not occur, the stress generated from the siliconerubber 10 causes a crack in the solder or other bonding materials.Therefore, the hardness of the silicone rubber 10 is desired to be 70 orless in Shore A hardness. Further, the hardness of the silicone rubber10 is preferred to be 10 or more in Shore A hardness to suppressgeneration of air bubbles from the lower side of the insulatingsubstrate 52 to secure firm adhesion to the base plate 1. As a result,the hardness of the silicone rubber 10 is desired to be 10 or more and70 or less in Shore A hardness.

In the semiconductor device configured as described above, the space 51surrounded by the base plate 1 and the insulating circuit board 5 andthe peripheral edge portion of the insulating circuit board 5 are filledwith the silicone rubber 10, and hence generation of air bubbles in thespace S1 can be suppressed. As a result, with the suppression ofseparation between the silicone rubber 10 and the base plate 1 in thespace S1, the insulation distance can be secured at the surface portionof the insulating circuit board 5, and thus the insulation reliabilityof the semiconductor device can be improved.

Second Embodiment

A second embodiment of the present invention differs from the firstembodiment in that a plurality of insulating circuit boards 5 used inthe first embodiment are arranged in the case. Other points are similarto those in the first embodiment, and hence detailed description thereofis omitted. Even when a plurality of insulating circuit boards arearranged in the case as described above, the peripheral edge portions ofthe insulating circuit boards are filled with silicone rubber, and hencethe insulation reliability of the semiconductor device can be improved.

FIG. 5 is a schematic top structure view for illustrating asemiconductor device according to a second embodiment of the presentinvention. FIG. 6 is a schematic sectional structure view forillustrating the semiconductor device according to the second embodimentof the present invention. FIG. 5 is a view for illustrating asemiconductor device 200 as viewed from the top through the first filler9 being a silicone composition. A peripheral edge portion (outerperipheral portion) of the insulating substrate 52, which is coveredwith the second filler 10 being a silicone composition, is indicated bythe dotted line.

Further, FIG. 6 is a schematic sectional structure view taken along thedash-dotted line B-B of FIG. 5. In FIG. 6, the semiconductor device 200includes the base plate 1, the case member 2, the solder 3 serving as abonding material, the semiconductor elements 4, the insulating circuitboard 5, the bonding wires 6 serving as wiring members, the electrodeterminals 7, the lid member 8, the first filler 9 being a siliconecomposition, the second filler 10 being a silicone composition, theelectrode patterns 51 and 53 serving as conductor layers, and theinsulating substrate 52. Further, the semiconductor device 200 has aconfiguration in which the plurality of insulating circuit boards 5 arearranged adjacent to each other.

The insulating circuit board 5 includes the insulating substrate 52, theelectrode pattern 51 formed on an upper face (front face) side of theinsulating substrate 52, and the electrode pattern 53 formed on a lowerface (back face) side of the insulating substrate 52. On the electrodepattern 51 formed on the upper face side of the insulating substrate 52,the semiconductor elements 4 are electrically bonded via the solder orother bonding materials 3. In this case, for example, as thesemiconductor element 4, a power control semiconductor element such as aMOSFET, which is configured to control a large current, or a diode forfree-wheeling is used.

Further, in the insulating circuit board 5, the electrode pattern 53formed on the lower face side of the insulating substrate 52 is fixed tothe base plate 1 via the solder or other bonding materials 3. Further,the base plate 1 serves as a bottom plate of the semiconductor device200 so as to form a region (hereinafter referred to as “case”)surrounded by the base plate 1 and the case member 2 arranged at theperiphery of the base plate 1.

For the purpose of securing an insulation property inside the regionsurrounded by the case member 2 of the semiconductor device 200, thefirst filler 9 being a silicone composition and the second filler 10being a silicone composition are injected into the case. The firstfiller 9 is, for example, a silicone gel, and is injected up to a heightthat allows the semiconductor elements 4 and the bonding wires 6 to besealed with the silicone gel 9.

Further, the second filler 10 being a silicone composition injectedbelow the silicone gel 9 in the case is, for example, silicone rubber,and is injected so as to surround a peripheral edge portion of theinsulating substrate 52. The silicone rubber 10 is injected up to afilling height position that is higher than an upper face of theinsulating substrate 52 from a front surface of the base plate 1, and islower than a bonding face between the semiconductor element 4 and thesolder 3, that is, a mounting surface (mounting portion) of thesemiconductor element 4, which is an upper face of the electrode pattern51 formed on the upper face side of the insulating substrate 52.

At this time, the silicone rubber 10 surrounds the peripheral edgeportion of the insulating substrate 52, and fills an exposed part of theinsulating substrate 52. The silicone rubber 10 is injected up to thesame height in a space between the plurality of electrode patterns 51formed on the upper face of the insulating substrate 52.

Further, the silicone gel 9 is injected onto the silicone rubber 10 sothat the case is filled with the filler.

FIG. 7 is a schematic sectional structure view for illustrating a spacebetween two insulating circuit boards in the semiconductor deviceaccording to the second embodiment of the present invention. In FIG. 7,a dimension between the two insulating substrates 52 is represented byL11, and a dimension between the electrode patterns 51 formed on the twoinsulating substrates 52 is represented by L10.

The dimension of L11 can be considered in the same manner as in the caseof the insulating substrate 52 and the case member 2 illustrated in FIG.3. L11 is generally a distance of 2 mm or more in consideration ofmisalignment at the time of bonding between the insulating circuit board5 and the base plate 1. In a case where L11 is 2 mm or less, when theinsulating circuit board 5 is arranged on the base plate 1, theinsulating circuit board 5 cannot be arranged at a predeterminedposition due to a shift during alignment.

Further, when L11 is 10 mm or more, a ratio of the silicone rubber 10occupied in the case is increased, which causes occurrence of stress.Thus, the silicone rubber 10 may be separated from the base plate 1.

The silicone rubber 10 injected into the space S1 between the base plate1 and the surface portion on the lower face side of the insulatingsubstrate 52 “adheres” to the insulating substrate 52 and the base plate1. The silicone gel 9 is brought into “close contact” with variousmembers, and has a characteristic in which the silicone gel 9 may bebrought into close contact again even after the silicone gel 9 isseparated from the members. Meanwhile, the silicone rubber 10 does notadhere to the members again after the silicone rubber 10 is onceseparated from the members.

The silicone rubber 10 has higher hardness than that of the silicone gel9, and has a tendency that separation is liable to occur due to stressthat occurs at an interface between the silicone rubber 10 and variousmembers due to a difference in linear expansion coefficient and anelastic modulus during the heat cycle applied to the semiconductordevice. Therefore, in a region of the silicone rubber 10 that isdirectly brought into contact with the base plate 1, the generatedstress can be suppressed by setting the distance L11 between the endportion of one insulating circuit board 5 and the end portion of anotherinsulating circuit board 5 to 10 mm or less, although the stress differsdepending on the hardness of the silicone rubber 10. Therefore, asemiconductor device having high insulation reliability can bemanufactured.

For those reasons, the dimension of L11 is set in a range of 2 mm ormore and 10 mm or less so that the semiconductor device having securedinsulation reliability can be configured.

In the semiconductor device configured as described above, the space S1surrounded by the base plate 1 and the insulating circuit board 5 andthe peripheral edge portion of the insulating circuit board 5 are filledwith the silicone rubber 10, and hence generation of air bubbles in thespace S1 can be suppressed. As a result, with the suppression ofseparation between the silicone rubber 10 and the base plate 1 in thespace S1, the insulation distance can be secured at the surface portionof the insulating circuit board 5, and thus the insulation reliabilityof the semiconductor device can be improved.

Further, even when the plurality of insulating circuit boards 5 arearranged in the case, the space between the plurality of insulatingcircuit boards 5 is filled with the silicone rubber 10, and hencegeneration of air bubbles can be suppressed between the plurality ofinsulating circuit boards 5. As a result, with the suppression ofseparation between the silicone rubber 10 and the base plate 1 betweenthe plurality of insulating circuit boards 5, the insulation distancecan be secured at the surface portion of the insulating circuit board 5,and thus the insulation reliability of the semiconductor device can beimproved.

Third Embodiment

A third embodiment of the present invention differs from of the firstembodiment in that the periphery of the insulating circuit board 5 usedin the first and second embodiments is surrounded by a partition wall.Other points are similar to those of the first embodiment, and hencedetailed description thereof is omitted. Through surrounding of theperiphery of the insulating circuit board by the partition wall asdescribed above, the insulation reliability is affected, and a region inwhich filling of silicone rubber is required is filled with the siliconerubber. Therefore, the insulation reliability of the semiconductordevice can be improved.

FIG. 8 is a schematic top structure view for illustrating asemiconductor device according to the third embodiment of the presentinvention. FIG. 9 is a schematic sectional structure view forillustrating the semiconductor device according to the third embodimentof the present invention. FIG. 8 and FIG. 9 are illustrations of a casein which the number of insulating circuit boards is 1.

FIG. 8 is a view for illustrating a semiconductor device 300 as viewedfrom the top through the first filler 9 being a silicone composition.The peripheral edge portion (outer peripheral portion) of the insulatingsubstrate 52 covered with the second filler 10 being a siliconecomposition is indicated by the dotted line. The partition wall 11 isformed so as to surround the insulating circuit board 5 along the entireperiphery of the outer peripheral portion (peripheral edge portion) ofthe insulating circuit board 5. The inner side of the partition wall 11is filled with the silicone rubber 10, and the outer side of thepartition wall 11 is filled with the silicone gel 9.

FIG. 9 is a schematic sectional structure view taken along thedash-dotted line C-C of FIG. 8. In FIG. 9, the semiconductor device 300includes the base plate 1, the case member 2, the solder 3 serving as abonding material, the semiconductor elements 4, the insulating circuitboard 5, the bonding wires 6 serving as wiring members, the electrodeterminals 7, the lid member 8, the first filler 9 being a siliconecomposition, the second filler 10 being a silicone composition, thepartition wall 11, the electrode patterns 51 and 53 serving as conductorlayers, and the insulating substrate 52.

Further, the partition wall 11 is formed around the outer peripheralportion (peripheral edge portion) of the insulating circuit board 5 soas to surround the insulating circuit board 5. The inner side of thepartition wall 11 is filled with the silicone rubber 10, and the outerside of the partition wall 11 is filled with the silicone gel 9.

For the partition wall 11, a thermoplastic resin and a thermosettingresin can be used. For example, as the thermosetting resin, a siliconeresin can be used, but the material is not particularly limited as longas the material can function as a dam wall for preventing the siliconerubber 10 from spreading, the material can maintain the shape in acuring temperature range of the silicone rubber 10, and the material hasa non-conductive property.

Along with the enlargement of the usage temperature range of thesemiconductor device 300 (to higher temperature or lower temperature),the silicone rubber 10 is more expanded or contracted as compared to therelated art by the heat cycle. When the area of the silicone rubber 10covering the base plate 1 is large, with the high stress generated dueto expansion or contraction of the silicone rubber 10, there is a riskthat the silicone rubber 10 may be separated from various members due toa difference in linear expansion coefficient between the silicone rubber10 and various members such as the base plate 1 and the solder 3 orother bonding materials.

For example, the coefficient of linear expansion of the silicone rubber10 is generally from 300 ppm/K to 400 ppm/K. When the hardness of thesilicone rubber 10 is higher than 70 in Shore A hardness, separationbetween the silicone rubber 10 and various members is liable to occur.

Further, even when separation between the silicone rubber 10 and thevarious members does not occur, the stress generated from the siliconerubber 10 causes a crack in the solder or other bonding materials.Therefore, the hardness of the silicone rubber 10 is desired to be 70 orless in Shore A hardness. Further, the hardness of the silicone rubber10 is preferred to be 10 or more in Shore A hardness to suppressgeneration of air bubbles from the lower side of the insulatingsubstrate 52 to secure firm adhesion to the base plate 1.

Even when the partition wall 11 is used as in the third embodiment,dielectric breakdown can be considered similarly to that in the case ofthe first and second embodiments. That is, this case is similar to thecase in which the case member 2 is replaced with the partition wall 11in FIG. 3. Therefore, the lengths L1, L2, L3, L4, and L5 are onlyrequired to be set so that the semiconductor device 300 can secure aninsulation distance satisfying the dielectric breakdown voltage.Further, the distance L6 between the partition wall 11 and theinsulating substrate 52 is generally 2 mm or more in consideration ofthe misalignment at the time of bonding between the insulating circuitboard 5 and the base plate 1. In a case where L6 is 2 mm or less, whenthe insulating circuit board 5 is arranged on the base plate 1, theinsulating circuit board 5 cannot be arranged at a predeterminedposition due to a shift during alignment. When L6 is 10 mm or more, aratio of the silicone rubber 10 occupied on the inner side of thepartition wall 11 is increased, which causes occurrence of stress. Thus,the silicone rubber 10 may be separated from the base plate 1. For thosereasons, the dimension of L6 is set in a range of 2 mm or more and 10 mmor less so that a semiconductor device having secured insulationreliability can be configured.

In the semiconductor device 300 according to the third embodiment, evenwhen the silicone rubber 10 has high hardness, with use of the partitionwall 11, the filling region of the silicone rubber 10 can be reduced ascompared to the cases of other embodiments of the present invention, andthe separation of the silicone rubber 10 from the base plate 1 or theinsulating circuit board 5 can be suppressed. In addition, generation ofa crack in the bonding material 3 can be suppressed, and with the effectof the silicone rubber 10, a semiconductor device having higherinsulation reliability as compared to the insulating characteristic ofthe semiconductor device 100 described in the first embodiment can bemanufactured.

In this case, the range of the distance between the partition wall 11and the end portion of the insulating substrate 52 is required to be setto be smaller than a range of 2 mm or more and 10 mm or less. The casein which the upper limit value is 10 mm is the same as the case in whichthe case member 2 is replaced with the partition wall 11, and the ratioof the silicone rubber 10 to be injected into the inner side of thepartition wall 11 is not decreased. Therefore, in order to decrease theratio of the silicone rubber 10 to be injected into the inner side ofthe partition wall 11, the upper limit value of the distance from theend portion of the insulating substrate 52 is required to be set to avalue smaller than 10 mm. For example, the distance can be set to 5 mmor less to decrease the ratio. When the ratio of the silicone rubber 10on the inner side of the partition wall 11 is to be decreased, thedistance from the end portion of the insulating substrate 52 to thepartition wall 11 is desired to be set in a range of 2 mm or more and 5mm or less.

FIG. 10 is a schematic top structure view for illustrating anothersemiconductor device according to the third embodiment of the presentinvention. FIG. 11 is a schematic sectional structure view forillustrating the semiconductor device according to the third embodimentof the present invention. FIG. 12 is a schematic top structure view forillustrating the partition wall of the semiconductor device according tothe third embodiment of the present invention. FIG. 10, FIG. 11, FIG. 12are illustrations of a case in which a plurality of (two) insulatingcircuit boards are provided.

FIG. 10 is a view for illustrating a semiconductor device 400 as viewedfrom the top through the first filler 9 being a silicone composition.The peripheral edge portion (outer peripheral portion) of the insulatingsubstrate 52 covered with the second filler 10 being a siliconecomposition is indicated by the dotted line.

In FIG. 10, the partition wall 11 is formed so as to surround theinsulating circuit board 5 along the entire periphery of the outerperipheral portion (peripheral edge portion) of the insulating circuitboard 5. The inner side of the partition wall 11 is filled with thesilicone rubber 10, and the outer side of the partition wall 11 isfilled with the silicone gel 9.

FIG. 11 is a schematic sectional structure view taken along thedash-dotted line D-D of FIG. 10. In FIG. 11, the semiconductor device400 includes the base plate 1, the case member 2, the solder 3 servingas a bonding material, the semiconductor elements 4, the insulatingcircuit boards 5, the bonding wires 6 serving as wiring members, theelectrode terminals 7, the lid member 8, the first filler 9 being asilicone composition, the second filler 10 being a silicone composition,the partition wall 11, the electrode patterns 51 and 53, and theinsulating substrates 52.

In the semiconductor device 400, two insulating circuit boards 5 arearranged as an example of a case in which a plurality of insulatingcircuit boards 5 are arranged in the case 2. The partition wall 11 isformed around the outer peripheral portion (peripheral edge portion) ofthe two insulating circuit boards 5 so as to surround the insulatingcircuit boards 5. The inner side of the partition wall 11 is filled withthe silicone rubber 10, and the outer side of the partition wall 11 isfilled with the silicone gel 9.

For the partition wall 11, a thermoplastic resin and a thermosettingresin can be used. For example, as the thermosetting resin, a siliconeresin can be used, but the material is not particularly limited as longas the material can function as a dam wall for preventing the siliconerubber 10 from spreading, the material can maintain the shape in acuring temperature range of the silicone rubber 10, and the material hasa non-conductive property.

As illustrated in FIG. 12, the partition wall 11 formed between the twoinsulating circuit boards 5 is shared by the two insulating circuitboards 5. The partition wall 11 has arrangement regions 111 forarranging the insulating circuit boards 5. The insulating circuit boards5 are arranged in the arrangement regions 111 while maintaining thedimension of L6. Further, as the partition wall 11, as illustrated inFIG. 9, the partition wall 11 may be arranged so as to surround theentire outer peripheral portion of each of the insulating circuit boards5 independently for the individual insulating circuit boards 5.

In the semiconductor device configured as described above, the space S1surrounded by the base plate 1 and the insulating circuit board 5 andthe peripheral edge portion of the insulating circuit board 5 are filledwith the silicone rubber 10, and hence generation of air bubbles in thespace S1 can be suppressed. As a result, with the suppression ofseparation between the silicone rubber 10 and the base plate 1 in thespace S1, the insulation distance can be secured at the surface portionof the insulating circuit board 5, and thus the insulation reliabilityof the semiconductor device can be improved.

Further, even when the plurality of insulating circuit boards 5 arearranged in the case, the space between the plurality of insulatingcircuit boards 5 is filled with the silicone rubber 10, and hencegeneration of air bubbles can be suppressed between the plurality ofinsulating circuit boards 5. As a result, with the suppression ofseparation between the silicone rubber 10 and the base plate 1 betweenthe plurality of insulating circuit boards 5, the insulation distancecan be secured at the surface portion of the insulating circuit board 5,and thus the insulation reliability of the semiconductor device can beimproved.

Further, the partition wall 11 is provided, and hence the region to befilled with the silicone rubber 10 can be minimized, and generation of acrack in the bonding material 3 can be suppressed. Thus, a semiconductordevice having higher insulation reliability as compared to theinsulating characteristic of the semiconductor device 100 described inthe first embodiment can be manufactured.

Fourth Embodiment

In a fourth embodiment of the present invention, the semiconductordevice according to any one of the above-mentioned first to thirdembodiments is applied to an electric power converter. The presentinvention is not limited to a specific electric power converter, but asthe fourth embodiment, a case in which the present invention is appliedto a three-phase inverter is described below.

FIG. 13 is a block diagram for illustrating a configuration of a powerconversion system to which an electric power converter according to thefourth embodiment of the present invention is applied.

The power conversion system illustrated in FIG. 13 includes a powersupply 1000, an electric power converter 2000, and a load 3000. Thepower supply 1000 is a DC power supply, and is configured to supply DCpower to the electric power converter 2000. Various power supplies canbe employed as the power supply 1000. For example, a DC system, a solarbattery, or a storage battery can be employed, or a rectifier circuit oran AC/DC converter connected to an AC system can be employed. Further,the power supply 1000 can be configured by a DC/DC converter configuredto convert DC power output from a DC system into predetermined power.

The electric power converter 2000 is a three-phase inverter connectedbetween the power supply 1000 and the load 3000, and is configured toconvert the DC power supplied from the power supply 1000 into AC powerto supply the AC power to the load 3000. As illustrated in FIG. 13, theelectric power converter 2000 includes a main conversion circuit 2001configured to convert the DC power into AC power to output the AC power,and a control circuit 2003 configured to output a control signal forcontrolling the main conversion circuit 2001 to the main conversioncircuit 2001.

The load 3000 is a three-phase electric motor to be driven by the ACpower supplied from the electric power converter 2000. The load 3000 isnot limited to a specific application, and may be an electric motormounted on various types of electric equipment. For example, the load3000 is used as an electric motor for a hybrid vehicle, an electricvehicle, a railway car, an elevator, or an air-conditioning apparatus.

Now, details of the electric power converter 2000 are described. Themain conversion circuit 2001 includes a switching element (not shown)and a free-wheeling diode (not shown), which are built in asemiconductor device 2002. When the switching element is switched, theDC power supplied from the power supply 1000 is converted into the ACpower, which is supplied to the load 3000. There are various types ofspecific circuit configurations of the main conversion circuit 2001, butthe main conversion circuit 2001 in the fourth embodiment is a two-levelthree-phase full-bridge circuit, which can be formed of six switchingelements and six free-wheeling diodes that are connected inanti-parallel to the respective switching elements. The main conversioncircuit 2001 includes the semiconductor device 2002 corresponding to anyone of the above-mentioned first to third embodiments, which includesthe built-in switching elements and the built-in free-wheeling diodes.Every two of the six switching elements are connected in series to formupper and lower arms. Each of the upper and lower arms forms each phase(U phase, V phase, or W phase) of the full-bridge circuit. Further,output terminals of the upper and lower arms, that is, three outputterminals of the main conversion circuit 2001 are connected to the load3000.

Further, the main conversion circuit 2001 includes a drive circuit (notshown) configured to drive each switching element. The drive circuit maybe built into the semiconductor device 2002, or a drive circuit may beprovided separately from the semiconductor device 2002. The drivecircuit is configured to generate a drive signal for driving theswitching elements of the main conversion circuit 2001, and to supplythe drive signal to control electrodes of the switching elements of themain conversion circuit 2001. Specifically, in response to the controlsignal from the control circuit 2003 to be described later, a drivesignal for turning on the switching element and a drive signal forturning off the switching element are output to the control electrodesof the switching elements. When the ON state of the switching element isto be maintained, the drive signal is a voltage signal (ON signal) thatis equal to or larger than a threshold voltage of the switching element,and when the OFF state of the switching element is to be maintained, thedrive signal is a voltage signal (OFF signal) that is equal to orsmaller than the threshold voltage of the switching element.

The control circuit 2003 controls the switching elements of the mainconversion circuit 2001 so that desired power is supplied to the load3000. Specifically, the control circuit 2003 calculates a time period(ON time period) in which each switching element of the main conversioncircuit 2001 is required to be in the ON state based on the power to besupplied to the load 3000. For example, the control circuit 2003 cancontrol the main conversion circuit 2001 based on PWM control ofmodulating the ON time period of the switching element in accordancewith the voltage to be output. Then, the control circuit 2003 outputs acontrol command (control signal) to the drive circuit of the mainconversion circuit 2001 so that an ON signal is output to the switchingelement to be brought into the ON state and an OFF signal is output tothe switching element to be brought into the OFF state at each timepoint. The drive circuit outputs the ON signal or the OFF signal as thedrive signal to the control electrode of each switching element inaccordance with this control signal.

In the electric power converter according to the fourth embodimentconfigured as described above, the semiconductor device according to anyone of the first to third embodiments is applied as the semiconductordevice 2002 of the main conversion circuit 2001, and hence thereliability can be improved.

In the fourth embodiment, description has been given of the example inwhich the present invention is applied to the two-level three-phaseinverter, but the present invention is not limited thereto. The presentinvention is applicable to various electric power converters. Althoughthe two-level electric power converter is employed in the fourthembodiment, a three-level or multi-level electric power converter may beemployed, and the present invention may be applied to a single-phaseinverter when power is to be supplied to a single-phase load. Further,when power is to be supplied to a DC load or the like, the presentinvention is applicable to a DC/DC converter or an AC/DC converter.

Further, the electric power converter to which the present invention isapplied is not limited to an electric power converter in which the loadis an electric motor as described above. For example, the electric powerconverter can be used as a power supply apparatus for an electricaldischarge machine, a laser beam processing machine, an induction heatingcooker, or a non-contact power feeding system. Further, the electricpower converter can be used as a power conditioner for, for example, asolar power system or an electricity storage system.

The embodiments described above should be regarded not as limiting butas exemplary in all respects. The scope of the present invention is notdefined by the scope of the embodiments described above, but is definedby the appended claims, and includes all equivalents and variations thatfall within the scope of the claims.

Further, the invention may be formed by combining a plurality ofcomponents disclosed in the above-mentioned embodiments as appropriate.

EXAMPLES

There are shown results of evaluating the initial insulatingcharacteristic of the semiconductor device and the insulatingcharacteristics thereof changed with the number of times of heat cycletest with use of evaluation samples (semiconductor devices) havingstructures corresponding to the first to third embodiments, whilechanging a rubber material to be injected, the height of the rubbermaterial to be injected, and a narrow gap region interval. The heatcycle test was conducted by placing the entire semiconductor device intoa constant temperature reservoir whose temperature was controllable, andrepeatedly changing the temperature of the constant temperaturereservoir in a range of from −40° C. to 180° C. In the heat cycle test,as one cycle, the evaluation sample is held at −40° C. for 30 minutesand then held at 200° C. for 30 minutes, and this cycle is repeated1,000 times.

Example 1

The evaluation sample corresponding to the first embodiment wasmanufactured as follows. The semiconductor element having a size of 11mm×12 mm and the insulating circuit board 5 (made of ceramic) having asize of 50 mm×60 mm were mounted on the base plate 1 being a metal platehaving a size of 100 mm×150 mm via the solder 3 serving as a bondingmaterial. As the bonding wires 6, aluminum wires having diameters of 0.4mm and 0.2 mm were used. On the metal plate 1, the case member 2 formedby insert molding was mounted with an adhesive, and then the siliconerubber 10 was injected up to various heights. The filling silicone gel 9having hardness of 70 in penetration was injected onto the upper surfaceof the silicone rubber 10.

In order to promote generation of air bubbles and occurrence ofseparation in the silicone gel 9, the semiconductor device formed of theabove-mentioned members was not subjected to decompression processingfor reducing air bubbles, and was manufactured by injecting the siliconegel 9 into the region surrounded by the case member 2 under atmosphericpressure, leaving the silicone gel 9 under atmospheric pressure for 30minutes, and then curing the silicone gel 9 at 90° C./1 hr. As resultsof the heat cycle test, the initial dielectric breakdown voltage and thedielectric breakdown voltages for every 250 cycles were measured.

In Table 1, there are shown results of the heat cycle test and resultsof external appearance observation of the evaluation sample having thestructure illustrated in FIG. 2, that is, the evaluation samplesmanufactured by injecting the silicone rubber 10 into the lower portionof the insulating substrate 52 of the semiconductor device 100.

FIG. 14 is a schematic sectional structure view for illustrating thefilling height of the silicone rubber at the peripheral edge portion ofthe insulating circuit board in Example of the present invention. Asillustrated in FIG. 14, the heat cycle test was conducted under fourconditions in which the respective filling heights of the siliconerubber 10 were 0 (none), H1 (height for covering two faces,specifically, the lower face and the side face of the insulating circuitboard 5), H2 (height for covering three faces, specifically, the lowerface, the side face, and the upper face of the insulating circuit board5), and H3 (height for covering three faces, specifically, the lowerface, the side face, and the upper face of the insulating circuit board5 and the wire bonding). Three semiconductor devices were evaluated ineach type of evaluations.

In Table 1, in the dielectric breakdown voltage test and the continuitytest conducted at the time of the heat cycle test, “∘” is noted foritems in which all three semiconductor devices passed the test, “Δ” isnoted for items in which one or two semiconductor devices passed thetest, and “×” is noted for items in which no semiconductor device passedthe test.

TABLE 1 Reliability test (heat cycle test: −40° C./200° C.) Number oftest cycles/cyc 0 250 500 1,000 Filling Dielectric ∘ x x x rubber:breakdown none voltage Continuity ∘ ∘ ∘ ∘ test Rubber Dielectric ∘ ∘ Δ Δheight: breakdown H1 voltage Continuity ∘ ∘ ∘ ∘ test Rubber Dielectric ∘∘ ∘ ∘ height: breakdown H2 voltage Continuity ∘ ∘ ∘ ∘ test RubberDielectric ∘ ∘ ∘ ∘ height: breakdown H3 voltage Continuity ∘ ∧ x x test

The test results shown in Table 1 are described. In the sample withoutthe silicone rubber, it was found that, when 250 cycles (cyc) of heatcycle test were conducted, air bubbles in the vicinity of the insulatingcircuit board were enlarged and the dielectric breakdown voltage wasdecreased. Further, in the sample in which the silicone rubber heightwas set to H1, it was found that the dielectric breakdown voltage wasdecreased when 500 cycles (cyc) of heat cycle test were conducted. Incontrast, in the sample in which the silicone rubber height was set toH2, it was found that the dielectric breakdown voltage was maintainedeven after 1,000 cycles (cyc) of heat cycle test were conducted.Further, in the sample in which the silicone rubber height was set toH3, it was found that continuity failure occurred due to bonding wiredisconnection when 250 cycles (cyc) of heat cycle test were conducted.

From the above-mentioned results, it has been found that, throughinjection of silicone rubber into the lower portion of the insulatingcircuit board of the semiconductor device, generation and enlargement ofair bubbles can suppressed, and the dielectric breakdown voltage canmaintained. Further, it has been found that a high effect can obtainedwhen the height of the silicone rubber is set to cover the end portionof the front-face electrode pattern at which the frequency of generationof air bubbles in the filler material is high, that is, to cover thethree faces, specifically, the lower face, the side face, and the upperface of the insulating substrate. Further, it has been found that wiredisconnection occurs when the wire bonding is covered.

Example 2

The evaluation samples corresponding to the first and second embodimentswere manufactured as follows. The semiconductor element having a size of11 mm×12 mm and the insulating circuit board (made of ceramic) having asize of 50 mm×60 mm were mounted on the base plate being a metal platehaving a size of 100 mm×150 mm through via the solder serving as abonding material. As the bonding wires, aluminum wires having diametersof 0.4 mm and 0.2 mm were used. On the metal plate, the case memberformed by insert molding was mounted with an adhesive, and then varioussilicone rubbers having different viscosities were injected. Thesilicone gel having hardness of 70 in penetration was injected onto theupper surface of the silicone rubber.

In Table 2, there are shown results of measuring initial partialdischarge characteristics after injecting various silicone rubbershaving viscosities of 80 Pa·s, 40 Pa·s, 20 Pa·s, 5 Pa·s, and 0.5 Pa·sinto the evaluation samples set to have three conditions of theelectrode pattern thickness of the insulating circuit board of 1,000 μm,500 μm, and 300 μm and four conditions of the creepage distance, whichcorresponds to the ceramic exposed portion of the insulating circuitboard, of 1 mm, 1.5 mm, 2 mm, and 2.5 mm.

TABLE 2 Partial discharge characteristic evaluation Creepage CreepageCreepage Creepage distance: distance: distance: distance: Narrow gapinterval 1 mm 1.5 mm 2 mm 2.5 mm Viscosity: Thickness: ∘ Δ x x  80 Pa ·s 1,000 μm Thickness: ∘ Δ x x   500 μm Thickness: Δ x x x   300 μmViscosity: Thickness: ∘ ∘ ∘ Δ  40 Pa · s 1,000 μm Thickness: ∘ ∘ Δ Δ  500 μm Thickness: ∘ Δ Δ Δ   300 μm Viscosity: Thickness: ∘ ∘ ∘ ∘  20Pa · s 1,000 μm Thickness: ∘ ∘ ∘ ∘   500 μm Thickness: ∘ ∘ ∘ ∘   300 μmViscosity: Thickness: ∘ ∘ ∘ ∘   5 Pa · s 1,000 μm Thickness: ∘ ∘ ∘ ∘  500 μm Thickness: ∘ ∘ ∘ ∘   300 μm Viscosity: Thickness: ∘ ∘ ∘ ∘ 0.5Pa · s 1,000 μm Thickness: ∘ ∘ ∘ ∘   500 μm Thickness: ∘ ∘ ∘ ∘   300 μm

Three semiconductor devices were evaluated in each type of evaluations.In Table 2, in the partial discharge measurement, “∘” is noted for itemsin which all three semiconductor devices passed the test, “Δ” is notedfor items in which one or two semiconductor devices passed the test, and“×” is noted for items in which no semiconductor device passed the test.

The test results shown in Table 2 are described. In the sample havingthe viscosity of the silicone rubber of 80 Pa·s, it has been found that,when the creepage distance is 1.5 mm or more, the partial dischargecharacteristic is decreased. Further, it has been found that the partialdischarge characteristic is decreased as the thickness of a portionbelow the substrate is decreased. The reason is considered to be becausethe silicone rubber was not able to be fully injected to the lowerportion of the insulating substrate, which is considered to be affectedby the filling performance into a portion having a small electrodepattern thickness and a long creepage distance, that is, the narrow gapregion.

A similar tendency was observed also in the sample having the viscosityof the silicone rubber of 40 Pa·s, and it has been found that thepartial discharge characteristic is decreased when the creepage distanceis 2 mm or more. In the sample having the viscosity of the siliconerubber of 20 Pa·s, it has been found that, even when a narrow gap regionhaving the creepage distance of 2 mm or more and the electrode patternthickness of 300 μm is was formed, a sufficient partial dischargecharacteristic is exhibited.

In the samples having the viscosities of the silicone rubber of 20 Pa·s,5 Pa·s, and 0.5 Pa·s, it has been found that, regardless of the creepagedistance and the electrode pattern thickness, a satisfactory partialdischarge characteristic is exhibited within a range evaluated thistime.

From the above-mentioned results, it has been found that, in asemiconductor device having a narrow gap region in which the creepagedistance of the insulating substrate of the semiconductor device is 1 mmor more and the filling height of the silicone rubber below the surfaceportion is 1 mm or less, a high partial discharge characteristic canmaintained when the viscosity of the silicone rubber to be injected intothe narrow gap is 20 Pa·s or less.

REFERENCE SIGNS LIST

-   1 base plate,-   2 case member,-   3 bonding material,-   4 semiconductor element,-   5 insulating circuit board,-   6 bonding wire,-   7 electrode terminal,-   8 lid member,-   9 silicone gel,-   10 silicone rubber,-   11 partition wall,-   51, 53 electrode pattern,-   52 insulating substrate,-   111 arrangement region,-   100, 200, 300, 400, 2002 semiconductor device,-   1000 power supply,-   2000 electric power converter,-   2001 main conversion circuit,-   2003 control circuit,-   3000 load.

The invention claimed is:
 1. A semiconductor device, comprising: aninsulating substrate having a conductor layer formed on each of an upperface and a lower face of the insulating substrate, the conductor layeron the upper face including a plurality of conductor layers in aplurality of areas, at least one of the plurality of conductor layers onthe upper face having a semiconductor element mounted thereon; a baseplate bonded to the conductor layer on the lower face; a case membersurrounding the insulating substrate and adhering to a surface of thebase plate to which the conductor layer on the lower face is bonded; afirst filler being a silicone composition injected into a regionsurrounded by the base plate and the case member; and a second fillerbeing a silicone composition that is harder than the first filler, thesecond filler being injected into a region surrounding a peripheral edgeportion of the insulating substrate and a region between the pluralityof conductor layers so as to cover an entirety of the upper face of theinsulating substrate in the region between the plurality of conductorlayers, the second filler being injected into a region below the firstfiller, the second filler being injected into a region in which a heightfrom the base plate is higher than the upper face and is lower than abonding face between the semiconductor element and the conductor layeron the upper face.
 2. The semiconductor device according to claim 1,wherein the second filler has a viscosity in a range from 0.5 Pa·s to 20Pa·s.
 3. The semiconductor device according to claim 1, wherein acreepage distance of the insulating substrate exposed from the conductorlayer is 1 mm or more, and wherein a distance from the base plate to asurface portion of a lower face of the insulating substrate, which isfilled with the second filler, is in a range from 0.3 mm to 1 mm.
 4. Thesemiconductor device according to claim 1, wherein an interval betweenthe case member and the insulating substrate is in a range from 2 mm to10 mm.
 5. The semiconductor device according to claim 1, wherein thesecond filler has a hardness in a range from 10 to 70 in Shore Ahardness.
 6. The semiconductor device according to claim 1, wherein thefirst filler has a hardness in a range from 20 to 100 in penetration. 7.The semiconductor device according to claim 1, wherein the insulatingsubstrate includes a plurality of insulating substrates bonded on thebase plate.
 8. The semiconductor device according to claim 7, wherein aninterval between the plurality of insulating substrates bonded on thebase plate is in a range from 2 mm to 10 mm.
 9. The semiconductor deviceaccording to claim 1, wherein the first filler includes a silicone gel,and wherein the second filler includes a silicone rubber.
 10. Anelectric power converter, comprising: a main conversion circuitincluding the semiconductor device of claim 1 and configured to convertpower input to the main conversion circuit to output power obtained bythe conversion; and a control circuit configured to output a controlsignal for controlling the main conversion circuit to the mainconversion circuit.
 11. A semiconductor device, comprising: aninsulating substrate having a conductor layer formed on each of an upperface and a lower face of the insulating substrate, the conductor layeron the upper face having a semiconductor element mounted thereon; a baseplate bonded to the conductor layer on the lower face; a case membersurrounding the insulating substrate and adhering to a surface of thebase plate to which the conductor layer on the lower face is bonded; afirst filler being a silicone composition injected into a regionsurrounded by the base plate and the case member; a second filler beinga silicone composition that is harder than the first filler, the secondfiller surrounding a peripheral edge portion of the insulating substratebelow the first filler in the region, the second filler being injectedinto a region in which a height from the base plate is higher than theupper face and is lower than a bonding face between the semiconductorelement and the conductor layer on the upper face; and a partition wallformed around an entire outer periphery of the insulating substrate, aninside of the partition wall being filled with the second filler. 12.The semiconductor device according to claim 11, wherein a distance froman end portion of the insulating substrate to the partition wall issmaller than an interval between the case member and the insulatingsubstrate, and is in a range of 2 mm or more and less than 10 mm. 13.The semiconductor device according to claim 11, wherein the secondfiller has a viscosity in a range from 0.5 Pa·s to 20 Pa·s.
 14. Thesemiconductor device according to claim 11, wherein a creepage distanceof the insulating substrate exposed from the conductor layer is 1 mm ormore, and wherein a distance from the base plate to a surface portion ofa lower face of the insulating substrate, which is filled with thesecond filler, is in a range from 0.3 mm to 1 mm.
 15. The semiconductordevice according to claim 11, wherein an interval between the casemember and the insulating substrate is in a range from 2 mm to 10 mm.16. The semiconductor device according to claim 11, wherein the secondfiller has a hardness in a range from 10 to 70 in Shore A hardness. 17.The semiconductor device according to claim 11, wherein the first fillerhas a hardness in a range from 20 to 100 in penetration.
 18. Thesemiconductor device according to claim 17, wherein an interval betweenthe plurality of insulating substrates bonded on the base plate is in arange from 2 mm to 10 mm.
 19. The semiconductor device according toclaim 11, wherein the insulating substrate includes a plurality ofinsulating substrates bonded on the base plate.
 20. The semiconductordevice according to claim 11, wherein the first filler includes asilicone gel, and wherein the second filler includes a silicone rubber.